1. Field of the Invention
The present invention relates to a process for producing high-purity 3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane (hereinafter referred to merely as “spiroglycol” or “SPG”) which is mainly usable as a raw material of resins.
2. Description of the Prior Art
Spiroglycol is produced, for example, through the steps of conducting an acetalization reaction of hydroxypivalaldehyde (hereinafter occasionally referred to merely as “HPA”) and pentaerythritol (hereinafter occasionally referred to merely as “PE”) in water in the presence of an acid catalyst, neutralizing with alkali, removing spiroglycol crystals precipitated during the reaction by filtration, washing with water and drying (JP 59-148776A).
Since the acetalization reaction is generally an equilibrium reaction under acidic conditions, the produced SPG undergoes decomposition reaction (reverse reaction). To avoid the decomposition of SPG, the acetalization reaction has been conducted in a solvent having a low dissolving power to SPG so as to allow the produced SPG to rapidly crystallize, thereby shifting the equilibrium to the product side. However, even by the use of the solvent having a low dissolving power to SPG, it is difficult to avoid the decomposition reaction because SPG dissolves in the raw materials to some extent. Other ways for avoiding the decomposition is to decrease the reaction temperature of the SPG synthesis and to use a large amount of solvent. However, these ways are industrially disadvantageous because lowered temperatures make the reaction slow and the use of a large amount of solvent requires large costs for treating waste liquids. Also, in many cases, rapid crystallization of SPG crystals fails to provide SPG crystals having a suitable particle size to allow the easy handling in industrial applications.
To increase the particle size, it has been proposed to produce SPG, for example, by allowing HPA and PE to react in water in the presence of an acid catalyst, neutralizing with alkali, heat-treating the resultant slurry mixture at 120° C. or higher (Japanese Patent 2796130). To reduce the amount of waste water, it has been proposed to produce SPG in a mixed solvent composed of water and an organic solvent immiscible with water in the presence of an acid catalyst (JP 2001-55388A).
In the processes of JP 59-148776A and Japanese Patent 2796130, the amount of waste water including filtrates after recovering SPG, washings, etc. reaches at least about 10 times the weight of SPG produced. The method of increasing the particle size as proposed in Japanese Patent 2796130 requires a re-heating step after the neutralization, to make the process complicated and increase energy consumption. In the process of JP 2001-55388A, although the amount of waste water is reduced, the resultant SPG has a purity as low as 98 to 99% and the used organic solvent should be separated and recovered. In any of the proposed processes, the yield of SPG is as low as 70 to 90 mol % because the raw materials and reaction intermediates remain in the reaction mother liquor after separating SPG crystals, and the environmental load is large in view of disposal of waste water and wastes, and energy consumption.
By reusing the filtrate after recovering SPG in the next run of reaction, the amount of waste water can be reduced and the yield of SPG can be improved. However, impurities are accumulated in the filtrate during its repeated use, to unfavorably cause the lowering of the purity and the reduction of particle size. If the alkali neutralization is conducted after the reaction, a large amount of acid must be required in the next reaction. In addition, the salts produced by the neutralization are accumulated in the mother liquor by its repeated reuse.
Under these circumstances, it has been proposed to directly obtain SPG crystals through the steps of filtration, washing with water, drying, etc. without employing the alkali neutralization. However, SPG produced by these conventional methods decomposes upon heating in the production of derivatives from SPG, to reduce the properties of the products. To avoid these problems, it has been proposed to further purify SPG by crystallization from organic solvents (JP 2000-7678A).